The present invention relates to the production of geminal dicarbamates.
Compounds having carbamate moieties are useful in that they can be converted to the corresponding isocyanates via known methods. For example, U.S. Pat. No. 4,388,246 discloses a method of thermally cleaving dicarbamates to form diisocyanates.
It has long been known that aldehydes but not simple ketones condense with carbamates directly to give geminal biscarbamates. See, e.g., J. Org. Chem., V. 10, pp. 145-8 (1941). It is also known to react aldehydes with unsaturated carbamates, e.g., H.sub.2 C.dbd.CH--CH.sub.2 --O--CONH.sub.2, to form geminal di(unsaturated) dicarbamates. U.S. Pat. Nos. 2,384,074; and 2,385,911. These synthetic techniques are of limited usefulness in that they can only be used to synthesize products having a hydrogen on the geminal carbon atom.
Joseph Hoch, in Vol. 210, Academie Sci. Compt. Rendu., pp. 560-2 (1935), teaches the preparation of isopropylidene-bis-(ethyl carbamate) in unspecified yield by reacting urethane (ethyl carbamate, H.sub.2 NCO.sub.2 C.sub.2 H.sub.5) with 2,2-diethoxypropane at from 105.degree. C.-190.degree. C., optionally in the presence of aniline chlorohydrate. Thus, this technique produced a geminal dicarbamate not having a hydrogen atom on the geminal carbon atom. However, it is disclosed that yield is reduced in the absence of aniline chlorohydrate.
It would be desirable to have a new, simple method for the high yield production of a large class of geminal dicarbamates, including compounds which do not have a hydrogen on the geminal carbon atom. Heretofore, such a method has not been disclosed.